Ignition system for free-piston engine



May 27, 1969 s. E. SORENSEN ETAL 3,446,197

IGNITION SYSTEM FOR FREE-PISTON ENGINE Original Filed Oct. 22, 1965 Sheet or s SVEND E. SORENSEN o a WILLIAM L. McHALE Fig. l mvsrvro'ns I BY 04am ATTORNEYS May 27, 1969 s. E. SORENSEN ETAL 3,446,197

IGNITION SYSTEM FOR FREE-PISTON ENGINE Original Filed Oct. 22, 1965 Sheet all I I17 Fig. 2

SVEND E. SORENSEN WILLIAM L. McHALE mvsurons May 27, 1969 s, SORENSEN ETAL 3,446,197

IGNITION SYSTEM FOR FREE-PISTON ENGINE Original Filed Oct. 22, 1965 Sheet 3 of a SVEND E. SORENSEN WILLIAM L. McHALE INVENTORS BYJ ,777aa. and

ATTORNEYS United States Patent Oflice 3,446,197 Patented May 27, 1969 ABSTRACT OF THE DISCLOSURE An ignition system especially adapted to a free-piston engine wherein a signal, generated by movement of the free piston with respect to a pick-up device, is amplified to provide sufiicient electrical energy to fire a spark plug. Preferably the pick-up device is positioned for activation by a working piston that is connected to the free piston.

Crass-reference to related application This application is a divisional application of US. patent application Ser. No. 501,719, entitled Free-Piston Engine Diaphragm Compressor and filed on Oct. 22, 1965, now Patent No. 3,386,647.

This invention relates to a compressor. More particularly, the invention concerns a free-piston engine, diaphragm compressor that is especially useful in a refrigeration system.

Briefly, this invention includes a free-piston engine that transmits energy to the diaphragm of a diaphragm compressor through an oil column. The diaphragm compressor provides a portion of the rebound energy for the free piston and other elements are provided that serve both the free-piston engine and the compressor to make the engine and compressor so interdependent and closely linked that they are essentially an integral unit.

One of the many problems of refrigerant compressors is sealing. Some movement of the usual compressor, either rotating or reciprocating, is required to compress the refrigerant gas. As a result there is customarily a seal of some sort involved in separating the power source from the compressor. This is especially true where the power source is, as it is in this invention, an internal-combustion engine. The sealing problem is greatly reduced, in this invention, from that of a dynamic seal to essentially a static seal, i.e., at a portion adjacent to the periphery of the diaphragm, by the diaphragm compressor.

Many electrically powered compressors are hermetically sealed with the power source enclosed in the system and acting in the atmosphere of the refrigerant. These systems also have problems since the sealed-in moving parts require lubrication. The oil in the refrigerant system has a tendency to coat and thereby insulate important heat transfer surfaces reducing the efiiciency of the system. The oil contamination problem is also eliminated in this invention by use of the diaphragm compressor. The oil column of this invention, which provides for the transfer of energy from the power source to the compressor, also provides lubrication for some of the moving parts of the power source.

An important advantage of the free-piston-engine diaphragm compressor is the reduction in weight and noise as compared to other refrigeration systems that must change rotary motion to reciprocating motion. In this invention, the engine motion and compressor motion are both reciprocating so that there is also a cost savings by the elimination of motion changing linkages and complicated force transfer apparatus.

It is an object of this invention to provide a refrigeration compressor driven by a free-piston engine that is capable of automatic operation including starting and stopping and that is especially useful for residential and similar installations.

It is another object of this invention to eliminate many of the parasitic features common to many conventional compressors such as excess friction, leakage, extra gadgets, complicated starting mechanisms, etc.

Still another object of this invention is to provide a dependable engine wherein carburetion and ignition are constructed to give reliable operation. The carburetion is accomplished by a construction that uses pressure changes from piston motion to supply the fuel already mixed with the air to the engine cylinder. The ignition system is a solid state ignition system that senses the piston position to fire the spark plug at precisely the right moment. The piston movement triggers a pick-up device by breaking a magnetic flux path to supply an input signal to a circuit (preferably transistorized) for producing a spark in the combustion cylinder. This is accomplished without the need for mechanical connection between the piston assembly and the ignition pick-up device. A particular orientation of the piston assembly is therefore not required. The ignition system of this invention does not depend upon breaker points, cam follower mechanisms or other moving parts (except the piston assembly) and consequently can operate for extremely long periods of time without replacement of parts.

Still another object of this invention is to provide a construction wherein the alignment problem for the reciprocating parts of the free-piston engine are largely eliminated.

Still another object of this invention is to provide a construction whereby the stroke-length of the piston assembly is held within close limits under all conditions of operation.

Still another object of this invention is to provide a construction whereby loss of refrigerant is virtually eliminated since an intermediate fluid (hydraulic) acting on the diaphragm performs the force transfer function between the engine and the compressor.

A still further object of this invention is to provide a construction whereby the unit is cycled at least once before an attempt is made to energize the ignition, such action effectively purging the engine thereby providing the starting reliability required.

A still further object of this invention is to provide a construction whereby the energy required for starting is generated during operation of the unit.

Still another object of the invention is to provide a detector that signals the starting system when the unit is running.

Still other objects and advantages of the invention will be apparent from the detailed description of the process and apparatus, the drawings and the claims that follow.

In the drawings:

FIG. 1 is a sectional elevational view of the free-pistonengine diaphragm compressor.

FIG. 2 is a sectional view of the ignition pick-up that triggers the high-tension circuit for firing the free-piston engine spark plug at the proper time.

FIG. 3 is a diagram of the high-tension circuit for firing the spark plug.

Referring to FIG. 1, the free-piston-engine diaphragm compressor 11, includes an engine section 13, and a compressor section that are closely connected. The free piston includes a power piston 17 connected to a compressor piston 19 'by means of a piston rod 21.'The power piston 17 reciprocates in an engine cylinder 23 having an inner liner 25. The power piston 17, provided with piston rings 27, divides the cylinder 23 into a combustion chamber 29 and a bounce and pumping chamber 31. The engine cylinder 23 is provided with a plurality of fins 33-33 for dissipating the heat of the combustion process. Oil, for lubrication of the power piston 17, is provided to a fitting 35 through a passage 37 connected to an oil ring 39 that surrounds the liner 25. The liner 25 is provided with a plurality of ports 41-41 for introducing the oil into the combustion chamber 29.

The cylinder head 43, which is preferably integrally cast with the engine cylinder 23, is provided with a spark plug 45 and a tap-off valve 47. The tap-oil valve 47 directs high pressure combustion products from the combustion chamber 29 to a storage tank (not shown) which is a part of the starting system for the free-piston engine 13.

The air and fuel are mixed together and enter the combustion chamber 29 through a plurality of intake ports 51-51. The exhaust ports 53-53 are preferably arranged with respect to the intake ports 51-51 to produce a loop scavenging or a Schnurle-type system, i.e., the intake ports 51-51 have a slanted entrance passage 55 that directs the air toward the wall of the combustion chamber 29 near the cylinder head 43 after which the air turns toward the exhaust ports 5353 forcing most of the gas from the previous cycle from the combustion chamber 29. (The port arrangement shown in FIG. 1 is for convenience only and is not the actual preferred arrangement.) The exhaust ports 53-53 communicate with an exhaust passage 57 which preferably is connected to a tuned expansion chamber (not shown) and a standard two-cycle automotive engine mufller (not shown).

The free-piston-engine diaphragm compressor. 11 is capable of operating with a variety of fuels. The embodiment shown in FIG. 1 is adapted for burning natural gas. A carburetor 59 is provided having an air intake opening 61. An annular fuel-air space 63 surrounds the bounce and pumping chamber 31 and communicates with bounce and pumping chamber 31 by means of ports 65-65 that are opened and closed by the trailing edge 67 of the piston 17. A passage 69 leads from the carburetor 59 to a reed valve plate 71 that has a plurality of reeds 73-73 that are activated by pressure differences to open and close a plurality of fuel-air ports 75-75.

When the power piston 17 is in the position shown in FIG. 1, the fuel-air space 63 communicates with the combustion chamber 29 through the intake ports 51-51, the intake ports 51-51 being opened when they are uncovered by the leading edge 77 of the power piston 17. As the piston 17 moves toward the cylinder head 43 on the compression stroke, the bounce and pumping chamber 31 becomes larger. (The bounce and pumping chamber 31 is defined by the end of the piston 17 at the trailing edge 67, the cylinder liner 25 and the seal section 79.)

When the trailing edge 67 of piston 17 moves to uncover ports 65-65, the chamber 31, which up to this point was acting as a more or less blind rebound chamber becomes a pumping chamber. At about the same time as ports 65-65 are opened, the leading edge 77 of piston 17 closes the intake ports 51-51. The continued enlargement of chamber 31 causes a reduction of pressure in chamber 31 causing the reed valves 73-73 to open and a stoichiometric mixture enters fuel-air space 63 and chamber 31. The mixture continues to enter until the piston 17 reaches top dead point position.

On the return or power stroke, the chamber 31 decreases in size, the valves 73-73 close, and the fuel-air mixture in the fuel-air space 63 is pressurized until the trailing edge 67 of piston 17 recloses port 65. At about the same time, the leading edge 77 opens ports 51-51 allowing the pressurized fuel-air mixture to flow into combustion chamber 29 scavenging the chamber 29 and supplying the fuel-air mixture for the next power stroke. After port 65 is closed, chamber 31 again becomes substantially a blind chamber and the gas compressed therein by the movement of piston 17 cushions the power stroke (along with the action of compressor 15) and supplies rebound energy to drive piston -17 back on the compression stroke.

A compressor cylinder section 81 is attached to the end of the engine cylinder 23 and is provided with a central bore 83 that flares into a bell-shaped section 85. The compressor piston 19 reciprocates in the central bore 83 and acts on a column of fluid 87 (preferably oil) that forms a coupling to transfer the motion of the piston 19 to the diaphragm 89. The central bore 83 is separated from the bounce and pumping chamber 31 by the seal section 79. The seal section 79 includes two interference shaft seals 91-91 that contact the piston rod 21 and substantially prevent leakage between chamber 31 and central bore 83. An annular space 93 is positioned between the seals 91-91 and is vented to the atmosphere through a passage 95 allowing any gases or oil that might leak by the seals 91-91 to escape. The seal section 79 fits against the end 97 of the cylinder lining 25 and against a shoulder 98 formed at the end of the cylinder section 81. Appropriate seals, such as O-ring seals 99-99, are positioned between the various surfaces of the cylinder liner 25, seal section 79, and cylinder section 81. A seal 101 is also provided between the engine cylinder 23 and the compressor cylinder section 81.

Reciprocation of the compressor piston 19 exerts a force on the fluid column 87. On the power stroke of the engine piston 17, the compressor piston 19 forces the fluid through a back-up plate 103 and against the diaphgram 89. The preferred embodiment of the back-up plate 103 is provided with an O-ring type seal 107 and a plurality of substantially radial slots 109-109. The surface 111 mounted toward the diaphragm 89 is concave to provide for the flexations of the diaphragm 89. The diaphragm 89 ordinarily will not contact the back-up plate 103 at maximum compressor suction stroke (when the compressor piston 19 is at top dead center), but during engine shut-off, the compressor gas pressure forces the diaphragm 89 against the concave surface 111 of back-up plate 103.

During the power stroke of the engine 13, when the piston 19 forces fluid through the back-up plate slots 109-109, the diaphragm 89 is moved to force compressor gas through a plurality of discharge valves 113-113 mounted in a valve plate 115. The valve plate 115 is provided with a concave surface 119 that is mounted toward the diaphragm 89. An O-ring type seal 121 is positioned on the valve plate 115. The seal 121 is positioned to be opposite seal 107 on the back-up plate 103 so that the seals 107 and 121 cooperate to hold and seal around the periphery of the diaphragm 89. Adjacent to the seal 107, a groove 123 is provided on the backup plate 103 and a groove 125 is provided adjacent seal 121 on the valve plate 115, which, together, form an annular space that permits the edge 127 of the diaphragm 89 to flip up and down as the diaphragm 89 flexes to pump the refrigerant gas.

The compressor intake valve 129 is centrally positioned in the valve plate 115. Slightly more area is provided for compressor discharge (six discharge valves 113113 are included in the embodiment of valve plate) than for intake since the power stroke of the engine 13 is somewhat faster than the rebound stroke. Two O-ring type seals 131 and 133 are positioned between the valve plate 115 and the compressor manifold 135. The seals 131 and 133 prevent leakage of the discharge gas to the intake gas-side and also leakage of the discharge gas from between the valve plate 115 and compressor manifold 135 to atmosphere.

The compressor manifold 135 is provided with a central inlet manifold 137 surrounded by an annular discharge manifold 139. An inlet line 141 connects the inlet manifold 137 to the evaporator (not shown) and a discharge line 143 connects the discharge manifold to the condenser (not shown).

Much of the expense in engines of this type is due to the alignment, tolerance and wear problems that are usually all closely related. The apparatus of this invention is constructed to avoid and eliminate some of these problems. Since the engine cylinder 23 and compressor cylinder section 81 are made separately and assembled, it follows that if these parts were perfectly aligned, the pistons 17 and 19 must be perfectly aligned. Although care is taken to establish and maintain good alignment, much of the problem is eliminated by a universal joint arrangement between the piston 17 and piston rod 21. The rod 21 fits into a space 145 in the piston 17. A washer 147 fits around the piston rod 21 and a nut 149 is threaded into the piston 17 holding the washer 147 in place. The piston 17 and rod 21 are always in compression (-by the combustion gases pushing the piston 17 toward the compressor 15 or the compressor gases pushing the piston 19,

via the diaphragm 89 and fluid column 87, toward the cyilnder head 43) and the washer 147 is only under very light loads if it is ever loaded at all. However, the important feature of the connection shown is that the piston rod 21 is not firmly attached to the piston 17 so that alignment and tolerance discrepancies are allowable. Further, tolerance of misalignment conditions is allowed by the construction of the compressor piston 19. Since the fluid column 87 is used as a force transfer medium, sealing re quirements are not as strict as they would be in other types of refrigerant compressors. When oil is used in the column 87, a leakage rate of about one gallon per hour can be tolerated. The oil merely passes by the piston 19 and out the passage 151 to an oil sump (not shown). A seal 153 is provided around the piston 19 to prevent excessive leakage. The piston 19 is also provided with a sleeve 155 selected from a material that is softer than the material of the piston 19. This feature centers the piston 19 in the bore 83. In addition, the soft material will catch any small foreign particles.

Since oil leakage around the piston 19 is permissible, the fluid lost from the fluid column 87 must be replaced on a regular basis. It was previously stated that the rebound for the engine piston 17 is provided in part by the chamber 31 and in part by the compressor gas exerting pressure on the diaphragm 89 and applying a force on the compressor piston 19 through the fluid column 87. The pressure in the bounce chamber 31 increases as the power stroke lengthens slightly due to a decrease of fluid in the column 87 or greater displacement of the diaphragm 89 due to a decrease in compressor load. The increased pressure in the bounce chamber 31 is used to activate the oil pump 157 which is insensitive to normal-length strokes but is activated when the pressure in the bounce chamber 31 increases due to less fluid in the column 87 and the resulting longer piston strokes. A port 159 is provided in the seal section 79 that communicates with the pump 157 through a passage 161.

The oil pump 157 fits into a threaded socket 167 and is provided with an intake 171 connected to an oil sump (not shown) and an outlet having a check valve 174 followed by a line 175 communicating with the oil column 87 The oil pump 157 operates when the oil column 87 needs oil. The reduction of oil in the oil column 87 decreases the resistance to the power stroke of piston 17, the power stroke lengthens slightly and the gas compressed in bounce chamber 31 takes on the increased rebound requirements by an increase in pressure. The increased pressure acting through passage 161 operates the pump 157. The pump 157 forces oil through check valve 174 and line 175 to replace the oil in oil column 87.

The timing for the ignition system is provided by positioning a pick-up device 223 to be triggered by the edge 225 of piston 19. FIG. 2 shows an enlargement of the pick-up 223 which includes a permanent magnet 227 surrounded by a coil 229. When the piston edge 225 passes the end of the permanent magnet 227 it breaks magnetic flux lines to produce a small electric current in coil 229 that triggers a high tension circuit 231 (shown in FIG. 3) that fires the spark plug 45. The cylinder section 81 has a socket 233 and an opening 235 for the end of the magnet 227 allowing the magnet 227 to be positioned very close to the piston 19. A seal 237 is provided around the pick-up casing 239, and the pick-up 223 is positioned and held in place by a spacer 241 and a hollow nut 243 that is threadedly engaged with the cylinder section 81. The leads 245 and 247 from coil 229 are connected to the high tension circuit 231 through a threaded electrical socket 249 (shown in FIG. 1).

The coil 229 has one lead 247 connected to ground and the other lead 245 is connected to a capacitor 251 and a transistor 253. With no pulse or current flow from coil 229, transistor 253 is off causing the power source 255 voltage to be presented to the base of transistor 259 via resistor 257 causing transistor 259 to conduct. By voltage divider action of resistors 263 and 265, due to conduction of transistor 259, transistor 267 receives the proper biasing voltage causing it to conduct. Conduction of transistor 267 causes the capacitor 277 to be charged. If there is a pulse of current from coil 229, the pulse turns on transistor 253 and turns off transistor 259. Transistor 267 is also turned 011 since current flow through the resistor 263 and 265 is terminated. The diode 271 serves to back bias transistor 267 assuring the turn-off of transistor 267. Capacitor 277 discharges through the primary coil of the ignition coil 273 inducing a voltage in the secondary winding which creates a spark at the spark plug 45. The Zener diode 279 prevents destruction of transistor 267 should the spark plug 45 be disconnected. The resistor 275 and capacitor 251 serve to hold the transistor 253 on for a short time after the turn-on signal is received from the coil 229.

It will be understood, of course, that, while the forms of the invention herein shown and described constitute the preferred embodiments of the invention, it is not intended herein to illustrate all of the possible equivalent forms or ramifications of the invention. It will also be understood that the words used are words of description, rather than of limitation, and that various changes, such as changes in shape, relative size, and arrangement of parts may be substituted without departing from the spirit or scope of the invention herein disclosed.

What is claimed is:

1. An ignition system in combination engine, comprising:

(a) a free-piston engine;

(b) a working piston connected to the combustion piston of said free-piston engine, said working piston reciprocal in a working cylinder;

(c) a pick-up device including a permanent magnet surrounded by a coil, said pick-up device positioned with a free-piston in said working cylinder at a point where the edge 3 of the working piston breaks the magnetic flux lines of said permanent magnet, as said combustion piston 7 is near top and point position, to generate an electric References Cited signal; (d) a solid-state amplifier including at least one capaci- UNITED STATES PATENTS tor, capacitor charging means, and a coil, said solid- 3,08%001 4/1963 P et state amplifier connected to said pick-up device and 3,172,596 3/1965 King 123-46 XR receiving the electric signal from said pick-up de- 5 3,308,801 3/1967 f 123148 vice to discharge said at least one capacitor through 3,367,314 2/1968 Hlrosawa et 123 148 the primary winding of said coil to produce a high voltage current in the secondary winding of said coil; and

(e) spark means connected to said secondary winding 10 of said coil, said spark means positioned in the com- 123148 bustion chamber of said free-piston engine.

LAWRENCE M. GOODRIDGE, Primary Examiner. 

